The present invention relates to a low distortion magnetic transmitter and method of operating. The present invention comprises an improvement over Applicant""s prior U.S. Pat. No. 6,246,231 issued Jun. 12, 2001. In the prior patent, a three axis transmitter is placed on top of a thin permeable barrier placed on a conductive plate. Disclosure is made of operation of the device with or without the conductive plate. As disclosed, magnetic fields are attenuated in areas outside the volume where position and orientation measurements are to be conducted, particularly in areas where metallic objects are commonly found that might cause eddy current distortion.
Applicant has found that the performance of the device disclosed in Applicant""s prior patent may be improved through the addition of a current loop about the periphery of the transmitter to nullify edge effect fields while also eliminating undesired excitations in conductive materials below the transmitter as well as below and adjacent the desired operating volume.
The present invention relates to a low distortion magnetic transmitter and method of operating. The transmitter is intended to permit measuring the position of a receiving antenna with respect thereto using magnetic fields and, preferably, in six degrees of freedom. The six degrees of freedom are the three coordinate directions, x, y and z, and the three orientation aspects commonly described as pitch, roll and yaw.
The present invention includes the following interrelated objects, aspects and features:
(1) In a first embodiment of the present invention, a sandwich is made up of a three axis transmitter mounted on a permeable attenuator with a spacer interposed between the transmitter and the attenuator. The attenuator is mounted on top of a conductive plate. About the periphery of the conductive plate or the permeable attenuator, a compensation coil is provided that is driven by a compensation coil driver different from the transmitter driver.
(2) The compensation driver is operated in a manner described in greater detail below to energize the compensation coil in a way to optimize compensation for magnetic field edge effects. Aspects taken into account in determining how to energize the compensation driver include the number and configuration of the transmitter coils, the shape and thickness of the magnetic attenuator, and the relationship between the magnetic attenuator and the conductive plate on which it is placed.
(3) In a second embodiment, instead of a single compensation coil about the periphery of the conductive plate, a number of individual compensation coils may be arranged about the periphery of the conductive plate or permeable attenuator, with the configuration of the compensation coils being designed based upon the factors set forth above, namely, the number and configuration of the transmitter coils, the shape of the permeable attenuator, and the configuration of the conductive plate with regard thereto.
(4) The individual compensation coils in the second embodiment may be activated in tandem or individually to compensate for non-uniform magnetic edge fields caused by the non-symmetrical configuration of, for example, three transmitter coils or, for example, a square permeable attenuator rather than a circular permeable attenuator.
As such, it is a first object of the present invention to provide a low distortion magnetic transmitter and method of operating.
It is a further object of the present invention to provide such a device wherein a three axis flat transmitter is employed.
It is a still further object of the present invention to provide such a device in which the transmitter is placed on a thin permeable attenuator.
It is a yet further object of the present invention to provide such a device in which the permeable attenuator is placed on top of a conductive plate.
It is a yet further object of the present invention to provide such a device in which a conductive coil is located about the periphery of the permeable attenuator or conductive plate.
It is a still further object of the present invention, in another embodiment thereof, to provide a plurality of compensation coils about the periphery of the permeable attenuator or conductive plate.
It is a still further object of the present invention to provide separate drivers for the transmitters and conductive plate(s).
It is a still further object of the present invention to provide such an invention in which the method of operating is also claimed.
These and other objects, aspects and features of the present invention will be better understood from the following detailed description of the preferred embodiments when read in conjunction with the appended drawing figures.